1. Field of the Invention
This invention relates to magnetic recording, dual stripe, magnetoresistive (DSMR) read heads and more particularly to methods of forming such read heads.
2. Description of Related Art
Askar, Magnetic Disk Drive Technology: Heads, Media, Channel, Interfaces And Integration, IEEE Press Inc., (1996) pp. 142-146, describes DSMR sensors and exchange biasing.
U.S. Pat. No. 5,262,914 of Chen et al. for xe2x80x9cMagnetoresistive Head with Enhanced Exchange Bias Fieldxe2x80x9d describes a MnFe AntiFerro-Magnetic (AFM) bias layer in direct contact with a NiFe MR layer which in turn is in physical contact with an interdiffusion layer composed of a noble metal, with a 240xc2x0 C., 7 hour annealing process for thermally forming an interface between the AFM layer and the MR layer which produces an exchange bias field to the MR layer.
U.S. Pat. No. 5,406,433 of Smith for xe2x80x9cDual Magnetoresistive Head for Reproducing Very Narrow Track Width Short Wavelength Dataxe2x80x9d describes at Col. 5, line 54 to Col. 6, line 33 longitudinal biasing of MR elements in opposite directions by pinning at the ends of the elements by use of patterned exchange biasing. After an MR element is deposited a patterned exchange layer of FeMn is deposited over the two ends of the first MR element. Either during (1) deposition of the AFM FeMn exchange layer or (2) after annealing, a longitudinal magnetic field is applied to the structure to orient the exchange bias field in the selected longitudinal direction. After formation of a spacer and the second MR element, a second patterned ferrimagnetic (TbCo) exchange layer of a different material from the AFM FeMn layer is deposited over the two ends of the second MR element. A post deposition field in the opposite direction from the first field is applied to the TbCo layer so that there is opposite magnetization in the two MR elements.
U.S. Pat. No. 5,561,896 of Voegeli et al. for xe2x80x9cMethod of Fabricating Magnetoresistive Transducerxe2x80x9d teaches a Selective Pulse Interdiffusion (SPI) process during which areas destined to become biasing segments of an MagnetoResistive (MR) head are selectively heated using one or more electrical current pulses of short duration.
U.S. Pat. No. 5,684,658 of Shi et al. for xe2x80x9cHigh Track Density Dual Stripe Magnetoresistive (DMSR) Headxe2x80x9d shows a DSMR having a first anti-ferromagnetic (AFM) longitudinal biasing layer and a second anti-ferromagnetic (AFM) longitudinal biasing layer that are parallel, in contrast with the present invention as described at Col. 8, lines 20-39. The AFM materials include NiMn, CoCr, CoCrPt, CoCrTa, CoCrNi, CoCrPtNi, CoCrNiTa, etc.
U.S. Pat. No. 5,696,654 of Gill et al. for xe2x80x9cDual Element Magnetoresistive Sensor with Anti-Parallel Magnetization Directions for Magnetic State Stabilityxe2x80x9d describes a dual MR element sensor with two MR elements separated by a high resistivity, conductive spacer element. A layer of a hard bias material abutting the track edges of the MR2 element biases it longitudinally in one direction. The MR1 layer is biased by a pair of exchange bias layers (NiFe/NiMn or NiFe/NiO) abutting the track edges of the MR1 strip by exchange coupling in an opposite, i.e. antiparallel longitudinal direction.
U.S. Pat. No. 5,859,753 of Ohtsuka et al. for xe2x80x9cSpin Valve Magnetoresistive Head with Spun Valves Connected in Seriesxe2x80x9d that includes first and second magnetization pinning layers which are anti-parallel to each other including AFM layers one of which is NiMn that has a high blocking temperature and one of which if FeMn that has a low blocking temperature. At col. 10, lines 10-19xe2x80x9d. . . NiMn having a high blocking temperature is formed as the first antiferromagnetic layer . . . on the first magnetization pinning layer . . . at a temperature of 200xc2x0 to 300xc2x0 C. The NiMn is grown in a magnetic field H01 applied in the first direction. Thereafter, . . . FeMn is formed as the second antiferromagnetic layer . . . on the second magnetization spinning layer . . . at a temperature of around 160xc2x0 C. While applying a magnetic field H02 in the direction opposite to the first direction, the growth of FeMn is carried out.xe2x80x9d At Col. 10, lines 37-60 it is pointed out that an alternative process can employ a step of heating to the higher blocking temperature and application of field H01 which is followed by a step of heating to the lesser blocking temperature temperature and application of field H02 can be deferred until after formation of the AFM layers.
In accordance with this invention a method is provided for forming a DSMR head including forming a first ferromagnetic (FM) strip on a substrate with a first anti-FM (AFM) pinning layer over a portion of the first ferromagnetic strip, the first AFM pinning layer being composed of a first material. Then perform a first high temperature annealing step. Form a non-magnetic layer over the strip and the pinning layer, and form a second FM strip on the non-magnetic layer. Form a second AFM pinning layer over a portion of the second FM strip, with a second AFM pinning layer being composed identically of the first material. Perform a second high temperature annealing step on the first and second FM strips and the first and second pinning layers and the intermediate non-magnetic layer in the presence of a second magnetic field antiparallel to the first magnetic field. A head with NiFe FM strips and FeMn, or MnPt, etc, AFM layers for both strips is provided. Preferably, the first and second magnetoresistive strips are composed of NiFe, and the first and second antiferromagnetic pinning layers are composed of FeMn or MnPt. Preferably, the first high temperature annealing step is performed at a temperature of about 300xc2x0 C. for from about 50 minutes to about 5 hours, with an applied external field of about 2000 Oe, the second high temperature annealing step is performed at a temperature of about 250xc2x0 C. for a duration of about 1 hour, with an applied external field of about 2000 Oe, and a third high temperature annealing step is performed at a temperature of about 250xc2x0 C. for a duration of about 4 hours, with no applied external field after completion of the second high temperature annealing step.
In accordance with another aspect of this invention, a dual stripe, magnetoresistive head comprises a first ferromagnetic strips on a substrate, and a first antiferromagnetic pinning layer over a portion of the first ferro-magnetic stripe, the first antiferromagnetic pinning layer being composed of a first material magnetized in a first direction. There is an intermediate non-magnetic layer over the strips and the pinning layer. A second ferro-magnetic stripe overlies the intermediate non-magnetic layer and there is a second antiferromagnetic pinning layer over a portion of the second ferromagnetic strips, the second antiferromagnetic pinning layer being composed of the first material, the second pinning layer being magnetized in a direction antiparallel to the first magnetic field. Preferably, the first and second magnetoresistive stripes are composed of NiFe, and the first and second antiferromagnetic pinning layers are composed of a material selected from the group consisting of FeMn, MnPt, MnPdPt, and NiMn, wherein Hpin for the first stripe is about 287 Oe and Hc is about 177 Oe and Hpin/Hc is about 1.62, and Hpin for the second stripe is about 227 Oe and He is about 35 Oe and Hpin/Hc is about 6.5.
An advantage of this method is that the same antiferromagnetic material with high blocking temperature, e.g. NiMn or MnPt can be used in the applications where the magnetization directions of the two exchange-coupled layers need to be set at various angles between them.
The invention teaches an anti-parallel exchange biased DSMR device with two annealing steps to set two exchange bias layers in different directions.
Another advantage of this invention is that the third annealing step increases the pinning field of the second MR strip and restores the pinning field of the first MR strip.